Pros
Without a doubt, the ability to have unlimited free users was incredibly useful. We have a number of freelancers who work with us on a part time basis and we were able to give them all access to the CRM for free. This gives HubSpot a considerable edge over it's per-license competitors.
HubSpot's lightweight ecosystem allows you to link all sales, marketing and service information in one place, all with a very straightforward and easy to understand user interface (another of HubSpot's benefits).
On the Marketing side, HubSpot's email builder is simple, yet powerful, and allows us to create great emails to send out to our customer base. On the Sales side, the Outlook Add-in allows us to make sure all sales activity by all team members is being tracked and logged in the CRM, so we are able to track performance and customer interactions quickly and easily. The Service functionality has allowed us to build out a fully fledged help centre for our customers.
Cons
Some aspects of the software are a little incomplete and/or suffer from inexplicable lacks of functionality. Sadly HubSpot CRM is yet to completely separate itself from its past as solely a marketing automation tool. It is obvious that the entire system architecture has been built around the contact record object type, with several frustrating quirks arising as a result. For example, a lot of the workflow functionality differs depending on the object type in use; contact based workflows allow you to use future dates as a trigger (e.g. run workflow x days before y date), whereas Company and Deal based workflows do not.
There are also a number of fundamental functions that require the Professional tier license to access. These include but are not limited to calculated fields, multiple currencies, lead rotation automation and A|B testing on emails. Clearly I understand that you get what you pay for, but given that these are all indispensable functions of a CRM, it seems to render the 'Starter' tier entirely useless, forcing you to pay the higher price. That being said, I am grateful that calculated fields are now a Professional rather than a higher Enterprise feature.
One last frustration is the inability to have multiple users on different tiers within the same Hub. I would greatly appreciate the ability to give Starter licenses to some of my free users, to give them a little more functionality, however, I am only allowed to purchase more Pro licenses, which I can't afford.